There has been used a technique for comparing (i) input image data obtained by reading a document image with a scanner and (ii) a pre-registered image, so as to determine similarity between the input image data and the pre-registered image, and controlling a process (such as copy, transmission, and edition) to the input image data in accordance with the result of the determination.
Examples of a method for determining similarity include: a method in which a keyword is extracted from an image with OCR (Optical Character Reader) so as to carry out matching with the keyword; a method in which a target image is limited to an image with ruled lines and matching is carried out based on features of the ruled lines (see Patent Document 1 (Japanese Unexamined Patent Publication No. Tokukaihei 8-255236 (published on Oct. 1, 1996))); and a method in which similarity is determined based on distribution of color components of input image data and a reference image (see Patent Document 2 (Japanese Unexamined Patent Publication No. Tokukaihei 5-110815 (published on Apr. 30, 1993))). Furthermore, Patent Document 3 (Japanese Unexamined Patent Publication No. Tokukaihei 7-282088 (published on Oct. 27, 1995) discloses a technique in which a descriptor that is invariable to distortion caused by digitalization of an input document or to a difference between the input document and a matching document in a document database is generated based on characteristics of the input document, and matching between the input document and a document in the document database is performed using the descriptor and a descriptor database which stores descriptors and which indicates a list of documents including features from which descriptors are extracted. In the technique, when the descriptor database is scanned, votes for individual documents in the document database are accumulated, and a document with the largest number of votes obtained or a document whose number of votes obtained is over a certain threshold value is considered as a matching document.
Furthermore, Patent Document 4 (International Publication No. 2006/092957, pamphlet (published on Sep. 8, 2006) discloses a technique in which plural feature points are extracted from a digital image, a set of local feature points are determined out of the extracted feature points, a partial set of feature points is selected out of the determined set of local feature points, invariants relative to geometric transformation each as a value characterizing the selected partial set is calculated in accordance with plural combinations of feature points in the partial set, features are calculated by combining the calculated invariants, and a document or an image with the calculated features in a database is voted for, thereby searching a document or an image corresponding to the digital image.
Furthermore, an example of a technique for controlling a process for input image data in accordance with the result of similarity determination is as follows: in order to prevent forgery of paper currency or stock certificate by a color image forming apparatus, it is determined whether input image data is identical with image data such as paper currency or stock certificate (reference image) or not based on a pattern extracted from the input image data, and when the input image data is identical with the image data of the reference image, a specific pattern is given to an output image so as to specify the image forming apparatus that carries out copying, a copied image is daubed, or copying is prevented.
Furthermore, Patent Document 5 (Japanese Unexamined Patent Publication No. Tokukai 2004-202737 (published on Jul. 22, 2004)) discloses a technique in which, when it is determined that a specific image (or similar image) is included in a document, a predetermined error code is displayed on an operational section of a color copier, and a route for carrying a recording paper is switched so that the recording paper is output to a paper output tray having a covered lock mechanism. In the technique, when a formed image is not a specific document, a service person calls on a customer, unlocks the lock mechanism with use of a predetermined key card or a password, and takes out the recording paper inside the lock mechanism.
In the image processing apparatus for determining whether input image data is identical with image data of a reference image or not, limitation of accuracy in reading an image etc. may result in erroneous determination depending on conditions under which the image is read. For that reason, in a case where input image data that is not identical with image data of a reference image is wrongly determined as being image data of the reference image, in order to carry out a process for the input image data, it is necessary for an administrator (specific user; a specific person authorized to judge whether the result of similarity determination is appropriate or not, such as a person in charge of security in a corporation etc.) to confirm that the determination is an error and to make an operation to allow the process for the input image data.
However, out of the conventional techniques, in the technique for daubing a copied image, preventing copy, or giving a specific pattern to an output image when it is determined that input image data is identical with image data of the reference image, the input image data or a recording paper on which an image is formed according to the input image data is not stored. Consequently, it is impossible to confirm whether the result of the determination is appropriate or not afterward.
Furthermore, the technique of Patent Document 5 requires a paper output tray having a covered lock mechanism and a switching mechanism for switching between routes for carrying a recording paper, which requires an apparatus with a larger and more complex structure, and an increase in costs for the apparatus.
Furthermore, in a case where the result of the determination is appropriate, i.e., in a case where input image data is identical with data of a reference image whose copy is prohibited, a resource such as a printing paper, a toner or ink consumed in printing input image data, and electricity necessary for image formation is wasted, resulting in an increase in running costs.
Furthermore, the technique of Patent Document 5 is applicable to only an arrangement in which an image corresponding to input image data is formed on a recording paper, and is not applicable to an apparatus for transmitting (e.g. electronic distribution and facsimile transmission) or filing image data.
Furthermore, in the technique of Patent Document 5, whether the result of the determination is appropriate or not cannot be judged until a service person calls on a customer, unlocks the lock mechanism, takes out a recording paper on which a copied image is formed, and confirms the recording paper. Consequently, in the case where the input image data is not identical with image data of a reference image, it is impossible to obtain the recording paper on which the image is formed until the service person comes and confirms the recording paper, which is very inconvenient for a user. In addition, it is very troublesome for the service person because the service person must move to a place where the copier is installed, unlock the lock mechanism, and judge whether the result of the determination is appropriate or not.